Curtains have been used as shading means in green-houses successfully a number of years. the green-house curtain has replaced the previously common lime painting of the glass surfaces of the green-house, but has also involved other advantages. Thus it has been proved that the fall of cold air, which occurs when the ventilator doors are opened, is eliminated and a uniform ventilation and heat distribution is achieved. The sunshine entering through the open ventilator doors is stopped by the shading fabric, which is not the case with the common lime painting of the glass. As a result of this the supply of nutritive liquid to the plants can be kept more regular and at a lower level, at the same time as the difficult and risky job with the lime painting of the glass surfaces and also the removal of the paint, has been completely eliminated. The shading fabric has shown a way to regulate the climate of green-houses so that tolerable conditions for the staff and the plants are provided, which conditions have a direct influence upon the quantity and quality of the harvest. It is important that the green-house curtain can be moved, i.e. that it can be pulled up and draped, so that in a simple way it can be pulled across or aside for regulating the inlet of light at the same time as it should not be space-requiring when it is pulled up or draped.
The high costs for heating green-houses have forced demands for a better heat insulation, and wall facings with different types of foils alone or together with a ceiling covering of a shading curtain which hitherto have been used, have given relatively small heat savings. This mainly results from the low insulating power of these materials.
A heat insulating drapery is previously known through the Swedish Pat. No. 7504537-7, which rather discloses some type of a Venetian blind comprising a great number of axially interconnected hollow foil pieces, the longitudinal connection portions of which form the laths of the Venetian blind. It has been demonstrated that this drapery is not suitable in green-houses for many reason. One reason is that it cannot be draped, i.e. pulled together across the direction of the hollow foils, which is necessary because of the presence of different obstacles in a green-house, e.g. stiffening braces, irrigation tubes etc., which make it impossible to use draperys that can only be pulled or rolled up. It would of course be possible to arrange the drapery with the hollow foils vertically orientated, but in this case the natural thermal movement of the air will provide a flow of air in the hollow foils, which will eliminate the heat-insulating effect of the drapery. A further drawback is that it is difficult to connect the draperys tightly to each other, which means that a relatively high amount of heat can leak out between adjacent draperys. Another drawback is that the drapery is made of a plastic sheeting which is not water-transmitting. On the upper side of horizontally arranged draperys there can be so large an accumulation of condensing water that the draperys break and damage the plants.
The demands that should be made on a green-house curtain are as follows:
(1) it should have a high heat insulating capacity, PA1 (2) it should be made of a soft, strong and pliable material, PA1 (3) it should be rollable and drapeable, PA1 (4) the curtain layers should, when the curtain is rolled up or draped, lie close to each other without being obstructed by any connecting members therebetween, PA1 (5) it should be tight against thermal air flows, PA1 (6) but it should not be water-tight so that water accumulates on it, PA1 (7) it should be washable, PA1 (8) it should have a low weight per unit of area, PA1 (9) it should be possible to make it as an effective barrier against radiant heat.
This last demand has hitherto been impossible to fulfill simultaneously with the other demands, since good reflectors necessarily are very bright metallized surfaces, which do not have the softness and pliancy of e.g. a fabric. It would of course be possible to cover a soft, plastic foil material with a reflective layer, but if this is not absolutely smooth and bright the reflecting power is bad. A drawback of such materials that have a high reflecting power, as aluminized plastic foils and a similar materials, is their high tightness which make them similar to diffusion barriers, i.e. they have the opposite effect to what is required for green-house curtains.